Post-finasteride syndrome is now a recognized condition, affecting as many as 20 per cent of those taking finasteride.…The persistent sexual side-effects of finasteride may manifest after varying periods of taking the drug, or not until the drug is discontinued. It is not known why some men are susceptible to the potential adverse effects of finasteride, while others—the majority—are not affected.…Further research is needed on who is susceptible to the persistent, adverse side-effects of finasteride and on the underlying mechanisms of the medication.
—A Clinical Overview of Finasteride and Its Potential Causative Links to Long-term Side-effects: The Medical Independent, Jan. 22, 2015